1. Field of the Invention
The present invention relates to a regenerative heat exchanger system and an operating method for such regenerative heat exchanger system.
2. Description of the Prior Art
A regenerative heat exchanger system is generally advantageous in transferring heat energy from a heating gas having an extremely high temperature to a separate gas to be heated (hereinafter referred to as "medium gas").
FIG. 10 shows a conventional regenerative heat exchanger system. In the drawing, an insulating vessel 90 has a top portion equipped with a burner 92 for supplying high temperature heating gas. The insulating vessel 90 has an upper part defining an inside space 94 therein and a lower part accommodating a heat accumulator 96 made of bricks or the like. The insulating vessel 90 has a bottom portion provided with a passage 98 for permitting medium gas to flow in as well as permitting the heating gas to flow out. This passage 98 has an inlet 99 at a lower end thereof. Although not shown in the drawing, a source for medium gas is connected to the inlet 99 of the passage 98 through a valve 100. Furthermore, an outlet 102 is formed in a side wall of the insulating vessel 90 at a position adjacent to the inside space 94 for flowing the gas to be out of the vessel 90. This outlet 102 is connected to downstream equipment (not shown) through a valve 104.
This type of regenerative heat exchanger system is operated in the following manner.
(1) First of all, the burner 92 generates high temperature heating gas, which is then supplied downward through the space 94 to the heat accumulator 96. The heating gas flows downward through the heat accumulator 96 and goes out of the insulating vessel 90 after passing through the passage 98. A supply of high temperature heating gas from the burner 92 to the heat accumulator 96 continues for a predetermined time to heat up the heat accumulator 96 sufficiently.
(2) Next, a medium gas, such as argon gas, is supplied upward from the bottom of the heat accumulator 96 to pass through the heat accumulator 96, thereby transferring heat energy stored in the heat accumulator to the medium gas. The medium gas, having passed through the heat accumulator 96 and having been heated up to a high temperature, is flowed to downstream components through the outlet 102.
A typical disadvantage of this type of regenerative heat exchanger system is that the heat exchange between the heating gas and the medium gas causes reduction of temperature in the heat accumulator 96 with elapsing time. Accordingly, if a significant amount of time has passed, the medium gas will not have a sufficiently high temperature at the outlet 102. Consequently, it is normally difficult to stabilize or maintain the medium gas at a necessary temperature at the outlet 102 for a long time.
To solve this disadvantage, for example, there have been conventionally proposed the following two systems (A) and (B).
(A) Two regenerative heat exchangers, termed the first and second, are provided. In the beginning of operation, the first regenerative heat exchanger alone is put in operation because the satisfactory temperature is assured for the medium gas. However, the temperature of the medium gas flowing out of the first regenerative heat exchanger gradually decreases as time passes. When a predetermined time has passed, the second regenerative heat exchanger is put in operation to compensate for the temperature reduction of the first regenerative heat exchanger. In other words, the respective operation timing of the first and second regenerative heat exchanger are shifted relative to each other for stabilization of the medium gas temperature. The temperature of the medium gas is stabilized by mixing high and low temperature gas between the first and second regenerative heat exchanger. This method is, for example, disclosed in Japanese Patent Publication No. 61-285394.
(B) In the regenerative heat exchanger system of FIG. 10 a bypass passage connecting the inlet 99 and the outlet 102 directly is provided to allow a part of the medium gas to bypass the heat accumulator 96. The bypass gas is thereafter mixed at the outlet 102 with the non-bypass medium gas passing through the heat accumulator 96. Control of the bypass gas is performed in such a way that the flow of the bypass is reduced with elapsing time, thereby stabilizing the gas temperature flowing out of the valve 104.
However, the above two systems are disadvantageous in the following points. In accordance with the system (A), at least two regenerative heat exchangers must be provided. This will inevitably increase the overall size of the equipment. On the other hand, in accordance with the system (B), a part of the medium gas is made to bypass the heat accumulator 96 and not receive the heat energy of the high temperature heating gas. This will result in a lower thermal efficiency since the regenerative heat exchanger system is not fully utilized. Furthermore, since the bypass gas is not heated at all, its temperature remains at an extremely low temperature. If such cool bypass gas having a low temperature is mixed with the heated gas at a high temperature, the resultant temperature will vary widely even if the added bypass gas amount is small. Accordingly, it is difficult to control the temperature accurately.